In a wafer support tool used for batch type heat treatment, there has been generally adopted a design that plural wafers are inserted and held in parallel to one another in grooves of a structure called a boat, which has support poles with the grooves. Especially in heat treatment at 1000° C. or higher, SiC is generally adopted as material of a wafer support tool because of its heat resistance and other properties. A method is adopted to cut grooves directly in the support poles with a diamond cutter or the like.
Since limitation is, however, placed on a shape of a work piece in this method, it is difficult to work the work piece into an intricate shape such as a curved surface. There also arises a problem that burrs are easily generated on surfaces of the grooves during cutting operation. In addition, there arises a problem that difficulties are encountered in additional working for removing the generated burrs and in polishing for decreasing surface roughness of the grooves with which a wafer is brought in contact, so damages or slip dislocations occur on wafers in the contact portions with the boat during heat treatment (see JP-A 7-161654 and 8-107081). Since the support poles are easy to be broken during working, which requires great labor and a working time, leading to poor productivity and difficulty in cost reduction.
The batch type heat treatment is to heat treat many wafers at a time using resistance heating (with a heater). In recent years, in addition to the batch type heat treatment apparatus, there also has been used frequently an RTP (Rapid Thermal Processing) apparatus for single wafer treatment in which rapid heating and rapid cooling treatment is performed by the use of a lamp heating method or the like.
Examples of heat treatment using an RTP apparatus can include: heat treatment for annihilating defects on a wafer surface, heat treatment for annihilating oxygen donors, heat treatment for producing a shallow diffused layer (RTA: Rapid Thermal Annealing), heat treatment for producing a thin oxide film (RTO: Rapid Thermal Oxidation) or the like. Single wafer epitaxial growth and vapor phase growth for an insulating film or the like using lamp heating can be included in the heat treatment using an RTP apparatus in a broad sense.
In the RTP treatment, as in the batch type heat treatment apparatus, a wafer support tool (may be called “a susceptor”) for heat treatment is employed; therefore, a problem has remained unsolved that slip dislocations are easy to occur in contact portions of the wafer support tool with a wafer (see JP-A 2002-164300).